3OO HARRY DEAL TORREY. 



was suggested by Loeb, 1 though in a somewhat different form in 

 connection with a discussion of the function of the red pigment 

 granules of the circulation. 



The acceleration of proximal development in ligated pieces of 

 Corymorpha is connected, not so much with any effect the ligature 

 may have upon the supply of oxygen to the neighboring tissues, 

 as with the inhibitory factors of contact and necrotic change that 

 it introduces. The same factors may play a certain part in the 

 inhibitory effect of the ligature in Tubularia also. 



It will be remembered that if a piece of Tubularia or Cory- 

 morpha is ligated in the middle, development at the distal wound 

 does not exhibit the acceleration characteristic of development at 

 the proximal wound. This difference is to be explained, I believe, 

 in the following way. Inhibition of development at the ligature 

 on its proximal side hinders the utilization of a certain quantity 

 of substances that would be used up proximally were the ligature 

 not present. That the availability of this material for the distal 

 end does not obviously accelerate the development distally is 

 due, probably, to the initial acceleration of the distal over the 

 proximal development in the absence of the ligature, that is, 

 under conditions of active competition with the proximal end. 



VII. 



The considerations in the foregoing sections lead to the con- 

 clusion that the polarity of Corymorpha, of which the initial ac- 

 celeration just mentioned is one expression, is a product of con. 

 ditions under which the organism develops, changing as they 

 change; that it is essentially but an inclusive designation for 

 certain phenomena that depend upon both internal and external 

 conditions, all of which can be experimentally controlled. The 

 internal conditions appear in the effect of the continuity of tissue 

 in an intact stem, and the presence of the original hydranth on a 

 segment of stem, both inhibiting the development of a hydranth. 

 The external conditions are represented by oxygen, contact, and 

 necrotic changes such as are produced by ligatures. The first is 

 necessary to all development while the others inhibit the develop- 

 ment of the hydranth. 



'Loc. cit. 



